Patent GB-448224-A (GB)
Title: Improvements in the manufacture of plastic materials having a basis of a cellulose derivative
IPC: C08L1/12
Filed: 1935-11-13
Abstract: A process for the conversion of compositions of matter containing cellulose derivatives and plasticizers therefor comprises applying heat to the compositions while they are under p  pressure at a temperature higher than the conversion temperature and then reducing the temperature at which heat is applied to the conversion temperature and continuing to apply heat at that temperature until conversion is effected.  The conversion temperature is defined as the temperature at which the cellulose derivative and the plasticizer become substantially homogeneous. The invention is of particular value in pressing a stack of sheets of unconverted cellulose derivative composition to form a block from which sheets may subsequently be sliced.  The composition may have a basis of an organic ester of cellulose or a cellulose ether or cellulose nitrate. Examples of suitable plasticizers are aryl sulphonamides, alkyl phthalates, alkyl tartrates, alkoxy esters of polybasic organic acids, aliphatic or aryl esters of phosphoric acid.  Modifying agents such as camphor to effect " case-hardening " may be added.  The compositions may also contain pigments, filling materials, dyes or lakes, fire retardants, oily materials, waxes or natural or synthetic resins.  The ingredients of the composition are preferably mixed in the presence of a solvent for the cellulose derivative.  Examples of suitable solvents are given in the Specification.  The ingredients are mixed in a kneader or other mixing device and worked on malaxating rolls until the composition contains the desired amount of residual solvent.  The material may then be taken off the rolls as sheets which are stacked to form a block which may be 12--24" wide and 12--60" long.  The thickness of the block may vary from 1--12". The block is placed in a press, e.g. a hydraulic press comprising a steam heated piston head, side rails and a steam heated support for the block.  The support and piston head are preferably heated to the same temperature.  The side rails may also be heated.  A pressure of 100--150 lbs./sq. inch or more is applied.  The pressure causes an increase in temperature in the interior of the block.  The temperature in the interior of the block.  The temperature initially applied to the block may be 10--50 DEG  C. higher than the conversion temperature.  Before the outsides of the block have been deleteriously affected, the applied temperature is reduced to the conversion temperature.  The higher temperature may be applied for a period varying from 10 minutes to 3 hours.  The reduction to the conversion temperature should be effected gradually, e.g. a temperature of 121 DEG  C. might be reduced to 100 DEG  C. in 45 minutes.  The conversion temperature depends on the nature of the plasticizer and may vary from 90--150 DEG  C.  After the heat treatment the pressure is maintained and the block allowed to set. The block is then cooled by circulation of cooling medium.  A block 2\ba1/2\be" thick may be heated to 110 DEG  C. for 3 hours, allowed to set for 1 hour and cooled for 3 hours.  A block 4" thick may be heated for 7 hours, allowed to set for 2 hours and cooled for 7 hours.  In an example, 100 parts of cellulose acetate, 35 parts of dimethyl phthalate, 10 parts of triacetin, and if desired 1--10 parts of ethyl para-toluene sulphonamide are mixed in the presence of acetone, and worked on malaxating rolls until the desired consistency is attained.  Sheets are then stacked to a height of 2\ba1/2\be" and the block subjected to a pressure of 300 lbs./square inch in a hydraulic press, the support and piston head of which are heated to 121 DEG  C. for about 2\ba1/2\be hours and are then allowed to cool during a period of 45 minutes to 110 DEG C. at which they are maintained for 3\ba1/2\be hours.  The block is allowed to set for 2\ba1/2\be hours, and is cooled by circulation of cold water through the press.  Pressure is then removed.  Sheets may be sliced from the block for laminated glass or the block may be moulded, cut, crushed or ground for use in the manufacture of other articles.  Cellulose esters employed in the composition should preferably be anhydrous to avoid hydrolysis.ALSO:A process for the conversion of compositions containing cellulose derivatives and plasticizers therefor comprises applying heat to the compositions while they are under pressure at a temperature higher than the conversion temperature and then reducing the temperature at which heat is applied to the conversion temperature and continuing to apply heat at that temperature until conversion is effected.  The conversion temperature is defined as the temperature at which the cellulose derivative and the plasticizer become substantially homogeneous. The invention is of particular value in pressing a stack of sheets of unconverted cellulose derivative composition to form a block from which sheets may subsequently be sliced.  The composition may have a basis of an organic ester of cellulose or a cellulose ether or cellulose nitrate. The material is rolled into sheets which are stacked to form a block which may be 12"-24" wide and 12"-60" long.  The thickness of the block may vary from 1"-12".  The block is placed in a press, e.g. a hydraulic press comprising a steam heated piston head, side rails and a steam heated support for the block.  The support and piston head are preferably heated to the same temperature.  The side rails may also be heated.  A pressure of 100-150 lbs. sq. inch or more is applied.  The pressure causes an increase in temperature in the interior of the block.  The temperature initially applied to the block may be 10-50 DEG  C. higher than the conversion temperature. Before the outsides of the block have been deleteriously affected p the applied temperature is reduced to the conversion temperature. The higher temperature may be applied for a period varying from 10 minutes to 3 hours.  The reduction to the conversion temperature should be effected gradually, e.g. a temperature of 121 DEG  C. might be reduced to 110 DEG  C. in 4 minutes.  The conversion temperature depends on the nature of the plasticizer and may vary from 90-150 DEG C.  After the heat treatment the pressure is maintained and the block allowed to set.  The block is then cooled by circulation of cooling medium.  Sheets may be sliced from the block for laminated glass or the block may be moulded, cut, crushed or ground for use in the manufacture of other articles. Cellulose esters employed in the composition should preferably be anhydrous to avoid hydrolysis.